In many current and future systems light beams are modulated in a digital and/or analog fashion and are used as “optical carriers” of information. There are many reasons why light beams or optical carriers may be preferred in these applications. For example, as the data rate required of such channels increases, the high optical frequencies provide a tremendous improvement in available bandwidth over conventional electrical channels such as formed by wires and coaxial cables. In addition, the energy required to drive and carry high bandwidth signals can be reduced at optical frequencies. Furthermore, optical channels, even those propagating in free space (without waveguides such as optical fibers) can be packed closely and even intersect in space with greatly reduced crosstalk between channels.
Optical attenuators perform numerous tasks associated with optical signal transmission systems. One function of an attenuator is to reduce the intensity of an optical signal which enters a photosensitive component. Photosensitive components are affected by variations in light intensity. Therefore, an attenuator causes the light intensity to be within the dynamic range of the photosensitive components. By using an attenuator, damage to the component is precluded. Additionally, the component does not become insensitive to small changes in the optical signal.
In other applications, attenuators serve as noise discriminators by reducing the intensity of spurious signals received by the optical device to a level below the device's response threshold. Moreover, optical attenuators are used to reduce the power of optical signals from an input fiber to an output fiber, and especially to balance optical power between several lines of an optical system. Many optical attenuators are also capable of actively attenuating an optical signal. Variable attenuators are required in some applications where different optical components require dissimilar incident optical signals, and hence variable sensitivities and saturation points. A fixed (i.e., passive) attenuation device is impractical for this purpose.
Attenuators serve to maintain the light level at a constant to compensate for component aging i.e., loss of efficiency in fiber amplifiers and reduced laser output from source, and changing absorption in optical waveguides. Variable attenuators serve to control feedback in optical amplifier control loops to maintain a constant output (e.g., as an automatic gain control element (AGC)).
Some variable attenuator designs require mechanical components or a number of optical components. Both of this type of attenuators exhibit a number of characteristics that are not desirable, such as high manufacturing and assembly costs, reduced reliability and extreme sensitivity to alignment.
There is a need for low loss, reliable variable optical attenuators.
A common problem encountered in applications in which high data rate information is modulated on optical carrier beams is the switching of the optical carriers from among an array of channels. These differing optical channels may represent, for example, routes to different processors, receiver locations, or antenna element modules. One approach to accomplish this switching is to extract the information from the optical carrier, use conventional electronic switches, and then re-modulate an optical carrier in the desired channel. However, from noise, space, and cost perspectives it is sometimes more desirable to directly switch the route of the optical carrier from the input channel to the desired channel, without converting to and from the electronic (or microwave) regimes.
A problem that is typical in optical switching systems is the insertion loss they impose. Some switching systems divide the input signal power into many parts, and block (absorb) the ones that are not desired. Others use switches that are inefficient and absorb, scatter, or divert a significant part of the input signal.
A commonly utilized optical switch is a one input, two output switch, also referred to as a 1×2 switch. There is a need for low loss, reliable 1×2 switches.
It is one object of this invention to provide polarization insensitive variable optical attenuators and 1×2 switches.
It is another object of this invention to provide low loss, reliable 1×2 switches.
It is a further object of this invention to provide low loss, reliable variable optical attenuators.